In many communication systems, communications networks are used to exchange messages among several interacting nodes which are separated apart in space. There are many types of networks which may be classified in different aspects. In one example, the geographic scope of the network could be over a wide area, a metropolitan area, a local area, or a personal area, and the corresponding networks are designated as wide area network (WAN), metropolitan area network (MAN), local area network (LAN), or personal area network (PAN). Networks may also differ in the switching/routing technique used to interconnect the various network nodes and devices (e.g. circuit switching, packet switching, etc.), in the type of physical media employed for waveform propagation (e.g. wired vs. wireless), or in the set of communication protocols used (e.g. Internet protocol suite, SONET (Synchronous Optical Networking), Ethernet, wireless LAN protocols, etc.).
One important characteristic of communications networks is the choice of wired or wireless media for the transmission of electrical signals among the network nodes. In the case of wired networks, tangible physical media such as copper wire, coaxial cable, fiber optic cable, etc. are employed to propagate guided electromagnetic waveforms which carry message traffic over a distance. Wired networks are a traditional form of communications networks and may be favored for interconnection of fixed network elements or for bulk data transfer. For example, fiber optic cables are often the preferred transmission media for very high throughput transport applications over long distances between large network hubs, for example, bulk data transport across or between continents over the Earth's surface.
On the other hand, in many cases, wireless networks are preferred when the network elements are mobile with dynamic connectivity or if the network architecture is formed in an ad hoc, rather than fixed, topology. Wireless networks employ intangible physical media in an unguided propagation mode using electromagnetic waves in the radio, microwave, infrared, optical, etc. frequency bands. Wireless networks have the distinct advantage of facilitating user mobility and rapid field deployment compared to fixed wired networks. However, usage of wireless propagation requires significant active resource management among the network users and high levels of mutual coordination and cooperation for compatible spectrum utilization.
Wireless networks also require a mechanism to regulate user access to the shared radio spread spectrum. That is, wireless networks must utilize a multiple access protocol to arbitrate mutual access to the common radio spectrum. Types of multiple access protocols include frequency division multiple access (FDMA), time division multiple access (TDMA), code division multiple access (CDMA), orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA), etc. In addition to multiple access technique, wireless systems may be classified by the wireless protocol family used for user transmissions, network services, signaling, etc. For example, commonly used wireless protocols include Global System for Mobile Communications (GSM), cdmaONE (IS-95), cdma 2000-1x, cdma 2000 EV-DO (Evolution-Data Optimized), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), etc. In particular, UMTS includes various operational modes including wideband code division multiple access (WCDMA) as an air interface and high speed packet access (HSPA) as an enhanced packet data service.